Surfeit and deficit of sodium: evidence from studies of body sodium in rats.
The concept of a basal level of body sodium (Strauss' state 'between surfeit and deficit') was studied by means of body sodium measurements in rats on different sodium intakes, in some cases after diuretic pretreatment. At a certain level of body sodium, when sodium intake was just enough to allow for body growth, a sodium chloride load (followed by a zero sodium intake) was excreted more or less quantitatively in 24-48 h. In rats pretreated with an ample sodium intake, the load was excreted more quickly and some additional sodium was also excreted. In rats pretreated with diuretic and a zero sodium diet, body sodium was very low and a sodium chloride load was retained to an extent that was more or less appropriate to the deficit. In a subsidiary part of the study, rats pretreated with a low sodium intake and frusemide and continuing on frusemide during and after the load, excreted a sodium chloride load at much the same rate as rats given a load following pretreatment with a very low sodium diet alone (i.e. not given a diuretic); after excreting the load they were able to maintain a stable (though reduced) level of body sodium in spite of cessation of sodium intake. Rats pretreated with hydrochlorothiazide, and continuing on this drug during and after the load, had a continued loss of sodium after cessation of sodium intake. The results are discussed in the light of the Strauss concept and appear to confirm it. Basal body sodium is, by inference, identified as the level at which delivery of sodium to the distal tubule exactly equals distal sodium reabsorption.
Simpson
F O
FO
Wellcome Medical Research Institute, University of Otago Medical School, Dunedin, New Zealand.
Ledingham
J M
JM
D000818:Animals; D001823:Body Composition / Q000502:physiology*; D001835:Body Weight / Q000187:drug effects; D005665:Furosemide / Q000494:pharmacology; D006852:Hydrochlorothiazide / Q000494:pharmacology; D008297:Male; D009318:Natriuresis; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000172:deficiency / Q000378:metabolism*
D006852:Hydrochlorothiazide; D005665:Furosemide; D012964:Sodium